The prior art contains several examples of door-mounted security peepholes or viewing ports for establishing visual contact, allowing an indoor observer to view an area exterior to an entrance door. An example of a viewing assembly for a door is described in U.S. Pat. No. 4,763,444 to Ritchie, comprising a glass mounted between an inner and outer bezel, with a mirror on the outer bezel for reflecting images through the glass to an observer. A hinged cover over the inner bezel can be lifted by the observer when it is desired to view the exterior area. However, a disadvantage in this arrangement is that a visitor at the door entrance may establish visual contact with the observer, and this may be undesirable in certain circumstances.
U.S. Pat. No. 4,571,901 to Morris et al., describes a vandal-resistant security viewing port for permitting observation into a cell, and while a large viewing area is provided for the observer, again, an undesirable feature is that two-way visual contact with a visitor may be established. In U.S. Pat. No. 4,050,792 to Svensson, there is disclosed an observation port assembly comprising separate optical viewing elements each having an inner optical axis at an angle to an adjacent optical viewing element such that each provides a partial view of the exterior area. The individual optical elements do not provide for visual contact by the visitor with the observer, however, the field of view provided by any one of them is limited.
A viewing port for doors including a light polarizing assembly is described in U.S. Pat. No. 4,719,720 to Olsen. The light polarizing assembly comprises two linear polarized optical elements which are mounted for rotation with respect to one another to change the viewing port from light-passing to light-blocking or a reduced light transmission condition. The outer optical element may be half silvered on the front, reducing visibility from the exterior of the door to practically zero so that no visual contact is established on the part of the visitor with the observer. Visibility from the interior is also reduced due to the half-silver layer on the outer optical element, and the only means provided for controlling the residual light level is a handle for rotating the outer optical element, which comprises a polarizing disc. Since the residual light level depends upon the lighting conditions interior of the door and exterior thereto, the possibility exists that the observer will not be able to easily identify the visitor, because of insufficient light even though a large, undistorted viewing area is provided.
In U.S. Pat. No. 4,561,116 to Neyret, a known inspection glass peephole mounted in a door is provided with a semi-reflecting surface on the interior of the door such that the observer may see a visitor outside the door whereat the visitor notices only the outer portion of the inspection glass. The inspection glass provided in this design affords the observer only a limited field of view, making it difficult for the observer to identify a visitor.
As indicated above, the security aspect associated with the construction of door peepholes must take into account the fact that the observer should be provided with the maximum viewing area, while visual contact on the part of the visitor must be eliminated. These requirements increase the security aspect as the observer can easily identify the visitor, without providing him with any visual information about the observer or the door interior area.
Therefore, it would be desirable to provide a door-mounted security peephole which provides a large, undistorted viewing area while eliminating visual contact on the part of the visitor independent of existing light conditions.